Here is are a couple of possible sons from NAA RecordSearch -
http://www.naa.gov.au/collection/search/CHRISTENSEN ROBERT MCEEAT : Service Number - Q111266 : Date of birth - 23 Sep 1917 : Place of birth - CAIRNS QLD : Place of enlistment - TOWNSVILLE QLD : Next of Kin - CHRISTENSEN ALBERT
CHRISTENSEN IVAN ERROL : Service Number - QX24921 : Date of birth - 15 Nov 1922 : Place of birth - MARYBOROUGH QLD : Place of enlistment - MARYBOROUGH QLD : Next of Kin - CHRISTENSEN ALBERT
Robert's death, from Ryerson Index
http://ryersonindex.net/search.php:
CHRISTENSEN Robert McFeat
Death notice
26JUN2011 Death [aged] 93
Cairns Post 02JUL2011
and Ivan Errol's:
CHRISTENSEN Ivan Errol
Death notice
08SEP1996 Death [aged] 73 at Maryborough, late of Point Vernon
Fraser Coast Chronicle (Hervey Bay) 09SEP1996
Albert served in WWII some capacity too
CHRISTENSEN ALBERT BENDIX : Service Number - Q220374 : Date of birth - 20 Oct 1892 : Place of birth - HOMEBUSH QLD : Place of enlistment - MT MOLLOY QLD : Next of Kin - CHRISTENSEN GRACE
PS Qld BDM online shows the 1922 death of a son of Albert & Grace was a from a different couple (Albert Jas & Grace Alice).
PPS There is definitely a connection between the CHRISTENSEN & McFEAT families but I am not sure if it is linked to your Albert? I suspect Robert McFeat CHRISTENSEN was actually the son of Albert CHRISTENSEN (a different one) & Helen McClay McFEAT. :-(
PPPS Sorry just discounted Ivan too!
http://www.queenslandfamilytrees.com/getperson.php?personID=I6450&tree=1